The guide pins on the pattern and the interlocking pattern on the cope and drags are there to ensure:

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The desired cavity in the final castings are formed

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The cope and drag are clamped together securely during the pouring of the molten metal.

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That the pattern can be easily taken out of the sand without damaging the cavity in the sand.

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The cavity in the sand in the cope and drag matches up to to form the intended geometry.

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There is adequate material to fill the cavity during the cooling and solidification of the molten metal.

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